1. Field of the Invention
The present invention relates to a color picture tube apparatus and, more particularly, to a color picture tube apparatus for displaying an image by time-dividing a single electron beam substantially into a plurality of beams.
2. Description of the Related Art
Generally, a color picture tube apparatus incorporates an electron gun assembly for emitting three electron beams. The three electron beams emitted from the electron gun assembly are deflected by a magnetic field generated by a deflecting unit. The deflected beams scan a phosphor screen opposing the electron gun assembly through a shadow mask in the horizontal and vertical directions, thereby displaying a color image on the screen.
In contrast to this color picture tube apparatus, Jpn. Pat. Appln. KOKAI Publication No. 61-263030 discloses a color picture tube apparatus in which a single electron beam is emitted from a cathode and time-divided substantially into three electron beams, thereby displaying an image.
More specifically, as shown in FIG. 1, this color picture tube apparatus has an electron gun comprising one cathode K for emitting a single electron beam 1, first, second, third, fourth, and fifth grids (only a fourth grid G4 is shown in FIG. 1) which are arranged between the cathode K and a phosphor screen 2 and control, accelerate, and focus the electron beam or electron beam segment(s) emitted from the cathode K, and a convergence electrode C. In this apparatus, the fourth grid G4 is constituted by two electrodes opposing each other as the first auxiliary deflecting means. The single electron beam 1 from the cathode K is electrostatically deflected by the first auxiliary deflecting means in three steps in a direction to separate from a tube axis Z, so that it is split into three beam segments. The convergence electrode C is constituted by a pair of central electrodes C1 serving as the second auxiliary deflecting means and a pair of two side electrodes C2 arranged on the two sides of the central electrodes C1. Each electron beam segment deflected by the first auxiliary deflecting means in the direction to separate from the tube axis is electrostatically deflected by the convergence electrode C in a direction to come close to the tube axis Z.
Referring to FIG. 1, reference numeral 5 denotes a main deflecting unit for deflecting the three beam segments; 6, a deflection center plane of the main deflecting unit 5; 7, a shadow mask; and 8, a three-color video signal switch for switching among red, green, and blue video signals.
According to this color picture tube apparatus, since the gap among the electron beam segments that are incident on the deflection center plane of the deflecting unit can be made small, a high-resolution, high-convergence color image can be displayed.
This color picture tube apparatus, however, has problems as follows. Namely, two auxiliary deflecting means are required for auxiliary deflection of the single electron beam emitted from the cathode. This increases the entire length of the picture tube and the deflecting power required for auxiliary deflection. Also, the manufacturing cost increases.
As described above, a color picture tube apparatus which time-divides a single electron beam substantially into three electron beam segments is conventionally known. However, since this color picture tube apparatus requires two auxiliary deflecting means for auxiliary deflection of the single electron beam, the entire length of the picture tube increases, and the deflecting power required for auxiliary deflection also increases. Again, the manufacturing cost rises.